a faint heart
1. A tendency to experience stress, fear, anxiety, sickness, or discomfort from unpleasantness, graphic imagery, physical strain, or risk. We must warn you that the following video contains images that may be unsuitable to those with a faint heart. I wouldn't advise reading the comments section of this article if you have a faint heart. Part of the hike is along a narrow path very close to a sheer cliff, so it's certainly not for anyone with a faint heart!
2. To have a very timid disposition; to lack the ambition or will to achieve success despite adversity. You can't have a faint heart if you want to work in this industry, I'll tell you that right now.